The present invention relates to a beam forming device for forming a uniform radiation beam and/or a uniform reception beam. The device is capable of radiating a search signal in a manner that the energy amount of the radiated signal is substantially the same at the same distance from the device within an angular range. The device is also capable of receiving incoming signals in such a way that electrical signals of the same amplitude level are produced based on signals of the same energy measured at a distance from the device, coming within an angular range.
The invention can be embodied in a beam forming device used in an underwater detection system for radiating or receiving ultrasonic wave signals, or in a radar apparatus for emitting or receiving electromagnetic waves.
Hereinafter, the invention will be explained as embodied in a beam forming device for radiating and/or receiving ultrasonic wave signals.
A prior art beam forming device comprises a transducer having electrodes. The device supplies the entire area of the electrode of the transducer with a signal having a constant amplitude level to radiate a resultant search signal, or receives incoming signals with the transducer. The directional characteristics of a radiation beam or a reception beam formed by the prior art device are shown in FIG. 27 wherein the vertical axis represents a radiation response level measured at the same distance from the device, or a reception response level measured at the receiving unit, and the horizontal axis represents an azimuthal angle. In radiation, FIG. 27 indicates that the signal strength of a radiated search signal in one direction is not the same as the one in another direction within an angular range. In reception, FIG. 27 shows that the amplitude of an electrical signal produced based on an ultrasonic signal of an energy level measured at a distance from the device coming in one direction is not the same as the one of another ultrasonic signal of the same energy level measured at the same distance, coming in another direction within an angular range.
With an underwater detection system employing the prior art beam forming device having the directional characteristics shown in FIG. 27, the incoming signals received thereby are displayed on the indicator unclearly and vaguely in their boundaries. Another drawback is that the size of a displayed image is enlarged or reduced when the amplification gain of the receiver for amplifying incoming signals is varied. This makes it difficult to exactly ascertain the size of the object being searched.